Important Note

Tufts ended funding for its Open Courseware initiative in 2014. We are now planning to retire this site on June 30, 2018. Content will be available for Tufts contributors after that date. If you have any questions about this please write to

Tufts OpenCourseware
Author: Ludwig von Hahn

I. An Overview

Understanding the growth and development of the human organism requires an understanding of nature and nurture, and the complex interplay between the two.

Implies a physical change, usually resulting from either an increase in cell number or cell size
A change or modification in a person’s capacity to function; the enhancement of a skill

Age-related norms for growth and development must be interpreted in context. The PATTERN of growth and development is much more important than the particular size of a child or the particular collection of developmental skills the child may possess at any given point in time.

II. Overview of Physical Growth

Growth in young people occurs in the following pattern:

  1. Relatively rapid growth during infancy with a gradual deceleration until about the fourth year of life
  2. A slow but uniform period of growth until puberty
  3. A prominent adolescent growth spurt
  4. A relatively gradual decrease in the rate of growth until completion of maturity, usually after age 20.

Differences in the size of adults between populations depends on differences in the gene pools of those populations as well as differences in environmental factors. There are differences in the size of Asians when compared to Caucasians, for example. However, Asians who grow up in the United States are generally taller and larger than Asians who grow up in Asia. Thus, genetic differences that may exist between these two populations can be mitigated by environmental factors.

Factors which affect growth are:

  1. Genetic factors.
  2. Maternal illnesses during pregnancy. Diabetes, endocrine diseases, diseases which affect placental sufficiency, etc., can affect foetal growth, even when these illnesses are adequately treated.
  3. Maternal and family socio-economic disadvantages during and after pregnancy. Poor nutrition, lack of access to prenatal care, poor education, and inadequate treatment of maternal illnesses can affect maternal health. These factors thus also affect the size of the newborn, and usually continue to affect the size of the child after birth.
  4. Maternal and family social/emotional problems during childhood. These factors, which may have affected the size of the newborn, can have an ongoing effect on the infant/child’s growth. Examples include poor nutrition and environmental or emotional deprivation. Emotional deprivation alone, or the absence of a stimulating environment, even in the presence of adequate nutrition, can result in growth failure. Notable examples of this occur in eastern European orphanages, where staff shortages result in minimal stimulation for the infants and children cared for at the orphanage.

Statistically speaking, the most important factor affecting a child's growth is her size at birth, and the factors that contributed to this. These factors tend to persist, and thus have an ongoing effect on growth.

Adolescent physical growth and development

Physiologically speaking, adolescence emerges as early as age 8 (girls) or 9 (boys), and as late as 14 in boys and girls. The two major events occurring during this time are a rapid increase in height and weight, and the development of sexual characteristics. Tanner staging is a method of evaluating the sexual maturity of an adolescent, and is based upon the appearance of secondary sexual characteristics (breast development in girls, penis and testicular development in boys, and pubic hair development in both). Sexual maturity is complete by the end of the teenage years.

III. Overview of Development

Brain Growth and Development

Nearly one half of the brain’s postnatal growth is achieved by the end of the first year, as witnessed by the impressive increase in head circumference. The enormous increase in head size is primarily accounted for by growth of the cerebral cortex. New cortical cells are added (neurons as well as dendritic cells), more connecting links are created, and cells become larger.

Myelination of brain cells (development of a sheath around each brain cell) is an important reason for the increase in head size as well. As different parts of the nervous system undergo myelination, the infant/toddler is capable of increasingly complex motor, verbal, and cognitive functions. The pattern of myelination results in a very predictable pattern of motor development:

  • cephalad to caudal (head to tail)
  • proximal to distal (from thorax to periphery)

Development in spheres other than the motor sphere is also predictable, but is not as clearly associated with myelinization patterns.

Development is divided into four major areas:

  1. Motor
  2. Speech/language
  3. Cognitive
  4. Social/emotional

A. Motor development

Motor milestones will be described in the lecture devoted to this topic. For the purposes of today’s lecture, it is sufficient to remember that motor development occurs in a cephalo-caudal, proximo-distal pattern. This means that the infant first achieves postural control of the head through control of the neck muscles, and is able to lift her head. Subsequently, she develops control of the shoulders, upper back, lower back, hips, etc. Arm and hand, and upper leg/lower leg motor control then also develops, subsequently extending to fingers and toes. The major accomplishments of the first year of life are the ability to stand, and the capacity for a pincer grasp. From here, motor development is programmed less from a biological/genetic perspective, and depends increasingly on environmental opportunities for refining and developing motor skills.

B. Speech and Language development

The development of speech and language skills also follow predictable patterns.

  1. Infant communication: proto-conversations, in which parent and infant take turns responding through facial gestures.
  2. Cooing: the infant makes vowel sounds
  3. Babbling: the infant makes consonant sounds. Arises prior to six months
  4. Jargon: speech-like sounds which include vowels, consonants, and prosody (the music of language) without actually using words. Arises prior to one year.
  5. Single words. Usually arise by age one.
  6. Two and three word sentences. Usually arise by age two.

The stages prior to jargon are largely biologically programmed. These abilities are present even if the environment does not provide a context for communication. However, jargon and words cannot develop without exposure to words. Thus, the neurobiological subtrate intended to produce speech (and motor skills for that matter) can only be “activated” if the infant is stimulated by his/her environment.

Depending on the degree of stimulation, the development of speech and language skills is potentially limitless. In medical school, you will learn a vast number of new words. The same holds true when learning a foreign language. These new words are linked to new concepts as well. The greater the demands of the environment, the greater the number of skills (words) that can potentially be acquired. The capacity of the brain to respond to this environmental stimulation does have limits, however. Not all people are able to learn the vocabulary of medical school, or of foreign languages, even if provided with the appropriate exposure.

C. Cognitive development: the work of Piaget

Piaget was the first child psychologist to map out child cognitive development in any detail. Much has been learned since he first published his work, and child psychologists have learned that the stages he presented are not necessarily acquired in the linear and ordered fashion he described. Nonetheless, his “map” of child development is still useful when attempting to understand various aspects of cognitive development.

Piaget divided child development into four stages:

1. Sensorimotor stage (ages 0 to 2)

In the sensorimotor stage, infants learn:

  1. About their own body movements
  2. That the movements of their body can have an effect on their environment
  3. To coordinate two or more movements or activities to reach a goal
  4. The concept of object permanence

The major cognitive development of the first two years of life is the acquisition of object permanence. The child can imagine an object, even when not seeing the object in front of him/herself. This is the start of representational thought.

2. The Preoperational stage: ages 2 to 4 or 5

"Operations" was a word Piaget coined to refer to ‘mental schemes’ or ‘mental strategies’. Today, these are perhaps better understood as neural schemes or neural connections. They come into play after the preschool years.

  1. Cause and Effect Relationships. Preschoolers establish cause and effect relationships between two events through their proximity in space or time. Any two events close in time or space are related causally. This is called transductive reasoning. In a preschooler’s mind, a child can catch any and all illnesses by being close to someone with an illness. A preschooler might say that a child who misbehaved one day and caught a cold the next day caught that cold because of the misbehaviour. Transductive reasoning persists in the adult population, where a “cold” is said to come from “being cold."
  2. The egocentricity of preschoolers. Preschoolers cannot understand that someone seeing an object from an angle different from themselves see the object differently from themselves.
  3. Preschoolers cannot apprehend more than one concept at a time. This is illustrated by the concept of conservation of volume. Preschoolers are not able to understand that a liter of fluid in a tall, narrow container is the same volume as a liter of fluid in a short, wide container. They cannot apprehend two aspects of a problem such as this, eg. width and length, simultaneously.

3. The concrete operational stage: ages 5 to 11 or 12

  1. The child learns operations such as:
    1. addition,
    2. subtraction,
    3. multiplication,
    4. division,
    5. serial ordering
  2. The child learns to conserve volume. Piaget considered this to be the major achievement of this age group. Conservation of number, substance, weight, and volume occur at different ages but in a specific order. There is a decline of egocentrism. Children at this stage are now able to imagine how others would perceive various situations.
  3. The child is unable to understand hypothetical situations. Children at the concrete stage of operations have great difficulty accepting hypothetical situations. They are not able to answer a question based on a hypothetical proposition. For example, if you asked a child at a concrete operational stage of thinking: "If all dogs were pink, what colour would your dog be?", they would not be able to answer the question. They might answer: "Dogs aren't pink."

4. The stage of formal operations: Adolescence and beyond

Instead of thinking only about real things and actual occurrences, the adolescent must start to think about imaginary things and possible occurrences. Adolescents learn how to

  • Use strategies for solving problems.
  • Accept a proposition that may be completely ridiculous and make arguments or conclusions from this proposition.
  • Understand abstractions (justice, liberty, etc.).
  • Think about their own thinking.